1. Field of the Invention
The present invention relates to a first structure intended for fastened assembly to a second structure, and in particular to such a first structure in which a cylinder-shaped fastener component having a knurled portion in its outer peripheral surface is embedded in a resin-made main body of the structure by insert molding, the first structure for example being one used in making a motor to be mounted on a vehicle the first structure having a brush holder and being adapted for fixing to a bracket of the motor housing.
2. Related Art Statement
As a structure for fixing a brush holder unit to a bracket of a motor housing in a motor to be mounted on a vehicle, there is widely employed a fixing structure in which, a plurality of cylinder-shaped fasteners having respective knurled portions in their outer peripheral surfaces are embedded in a brush holder stay molded of resin by insert molding, and, while this fastener insert structure (i.e., the brush holder stay) is abutted against an end surface of the bracket, a bolt is inserted through each fastener to be screwed into the bracket so that the brush holder stay is screwed on the bracket. Generally, the outer peripheral surface of the fastener to be inserted into the product molded of resin is knurled so that the fastener can bite into the resin more firmly.
As examples disclosing the above-described type of conventional fastener insert structure, there may be listed Japanese Patent Publication No. 63-3165, Japanese Patent Publication No. 47-11009, Japanese UtilityModel Laid-Open No. 51-157767, Japanese Utility Model Publication No. 48-20817, and Japanese Utility Model Publication No. 5-13660.
For example, Japanese Utility model Publication 5-13660 discloses a fastener insert structure in which, by insert molding, a screw member is embedded in a mounting member for joining wiper arms, and discloses such wiper pivot mounting structure that a nut or bolt is screwed into the screw member through a car body panel while an abutting surface of the screw member is abutted against the car body panel.
However, in a brush holder stay having a plurality of fasteners which are embedded in the stay and have knurled portions in respective outer peripheral surfaces, there maybe a case that, at the time of molding, molding resin flows along knurled grooves to adhere to a fastener's end surface serving as a seating surface on a bracket. As a result, when a bolt is inserted through each fastener and screwed while each fastener's seating surface is abutted against the end surface of the bracket, there is fear that axial force of bolting is decreased because of deterioration of the resin by creep or the like. Further, in the case that a fastener is knurled in the whole outer peripheral surface, an end surface of the fastener tends to be deformed at the time of knurling, owing to plastic deformation of the material.
When the axial force of bolting is decreased, relative position between the brush holder stay and the motor bracket is changed, and accordingly, sliding contact between the brush and the commutator becomes unstable, and there is fear of arc etc.
An object of the present invention is to provide a fastener insert structure which can prevent adhesion of resin to a seating surface of a fastener.